I. Field of the Invention
This invention relates to the field of biofuel production, and in particular to the removal of tars from synthesis gas produced from biomass feedstock.
II. Description of the Related Art
Tars are generated in the gasification of biomass and other carbonaceous feedstocks to produce synthesis gas. Tars are a significant impediment to the utilization of synthesis gas due to their tendency to condense and foul downstream equipment and deactivate catalysts.
Conventional aqueous scrubbing techniques can remove many of the tars from the synthesis gas, but generate a waste water stream, which requires significant downstream treatment, and the heavy polyaromatic hydrocarbons (PAH) tars can precipitate and foul the scrubbing equipment. In addition, synthesis gas produced by aqueous scrubbing is not suitable for some power and all chemical applications.
Rising fossil fuel prices have also generated increased interest in biodiesel. However, current processes for biodiesel production utilize methanol derived from relatively expensive fossil fuel sources, such as natural gas, and generate waste byproducts of lower value such as glycerol. Biodiesel and glycerol are produced from the transesterification of vegetable oils and fats with alcohol (methanol) in the presence of a catalyst (NaOH or KOH). About 10 wt % of the vegetable oil is converted into glycerol during the transesterification process. Crude glycerol has the following typical composition: 75 wt. % glycerol, 10 wt. % ash, 10 wt. % water and 5 wt. % other organic matter.
Glycerol markets are currently limited and an increase in biodiesel production would cause glycerol prices to decline further. At these low prices it would become less attractive to recover high purity glycerol from crude glycerol. Generally, purification of crude glycerol is energy intensive, such as purification via vacuum distillation.
Further improvements are needed to reduce cost and increase efficiency of biofuel production processes.